After the female fighter if you fall with the loose tiles you can see a passage going off to the right..

You'd need a float potion to get down there safely I think.

It has bugged me for 25 years and there's probably nothing there but I keep googling every few years to see if anyone figured it out.

Hey there and welcome!
There is nothing there, it's just death. I think all original games have those rooms, maybe to do people get curious or something, heh. SNES mods that I've played have those rooms too, I also made one of those rooms myself.

May the Moon light your path and together, we will open the way at Grand Clock.

You're welcome!
Yes. Since there is no way we can do that, we can only put a Slow Down Potion by editing the game, otherwise is use a GameShark or something. But is useless since we'll die, anyway. It's just to kill the curiosity
That room to the right is a 255 or 254 and each level have 24 rooms: 0 to 23, so those 255 or 254 will lead us to death, you know? Unless to create ceilings or walls to the left like, 255 at up will be a ceiling, 254 it's a open ceiling (like sky) and to make a wall to the left would be like:
--------------255 (ceiling)
(wall) 255 - 0 - 255 (death)
--------------255 (death)
0 is the room where you are.

Of couser if you use walls by editing to the right and tiles to down, you'll never die. That means there are no paths, just find another way to go ahead.
That would be more easy with pics, but I don't have my PC right now and also, I don't speak English and that maybe get you confuse.
The better thing for you is watch the tutorials videos that you can find here or on popot site.

May the Moon light your path and together, we will open the way at Grand Clock.

There are similar level designs on level 9 (before the shadow), on level 11 (the first pit you meet), and on level 12.
The one on level 9 is a bit different, though: it goes off to the left, and there is an actual extra room you could enter.
You can find maps here: http://vgmaps.com/Atlas/SuperNES/index. ... ceOfPersia